In a magnetic disk drive such as for a hard disk, when a vibration such as a rotation vibration is exerted thereon from the outside, an external disturbance (“disturbance”) resulting from the vibration acts on a position control system of a magnetic head, thereby leading to inhibition of positioning of the magnetic head. Hence, a countermeasure is taken to suppress degradation of a position error resulting from the disturbance caused by the external vibration.
As one countermeasure as mentioned above, a technique utilizing a chasing peak filter is disclosed in Japanese Patent Publication No. 2003-109335 (“Patent Publication 1”). This technique progressively causes approximation of the peak frequency of the peak filter to the frequency of the disturbance, thereby to suppress the disturbance that acts on the position control system of the magnetic head.
According to the technique utilizing the chasing peak filter, a parameter of the peak filter is updated on the basis of a sample or predetermined sample of an error signal indicative of the position error of the magnetic head during track following, which causes the magnetic head to follow tracks of the magnetic disk.
In this case, however, since the parameter has to be updated by taking stability of the peak filter into consideration, an update range of the peak frequency is restricted, and hence it takes time until the disturbance is suppressed.
Further, for magnetic disk drives, a burden of calculations necessary to suppress disturbances as described above, is required to be reduced.